#include <stdio.h>

char *My_strcat(char *demo, char *M3)
{
    char *yknow = demo;
    while (*demo)
    {
        demo++;
    }
    while (*demo = *M3)
    {
        demo++;
        M3++;
    }
    return yknow;
}

int main(int argc, char const *argv[])
{
    char arr[10] = "123";
    char arr1[10] = "234";
    printf("%s", My_strcat(arr, arr1));
    return 0;
}
